Tag Archives: California Department of Toxic Substances Control

Nanosilver history

According to Empa researchers, Bernd Nowack and Harald Krug, together with Murray Heights of the company HeiQ, silver at the nanoscale has a long history. From the Jan. 31,2011 news item on physorg.com,

Nanosilver is not a new discovery by nanotechnologists — it has been used in various products for over a hundred years, as is shown by a new Empa study. The antimicrobial effects of minute silver particles, which were then known as “colloidal silver,” were known from the earliest days of its use.

Their paper showing that nanosilver is not a 21st century discovery is being published in Environmental Science & Technology. From the news item,

Silver particles with diameters of seven to nine nm were mentioned as early as 1889. They were used in medications or as biocides to prevent the growth of bacteria on surfaces, for example in antibacterial water filters or in algaecides for swimming pools.

The nanoparticles were known as “colloidal silver” in those days, but what was meant was the same then as now – extremely small particles of silver. The only new aspect is the use today of the prefix “nano”. “However,” according to Bernd Nowack, “nano does not mean something new, and nor does it mean something that is harmful.” When “colloidal silver” became available on the market in large quantities in the 1920s it was the topic of numerous studies and subject to appropriate regulation by the authorities. [emphasis mine]

This suggests that there has been sufficient research on what we now call nano silver and its impact on the environment and on health. By contrast, the California Department of Toxic Substances Control (DTSC) had this to say in its recent call for information about analytical test methods for nanomaterials (from the Dec. 27, 2010 news item on Nanowerk),

Nano Silver

Nano silver is used increasingly in many consumer products. These include food contact materials (storage containers, cups, bowls and cutting boards), children’s toys and infant products, disinfectants, cosmetics, cleaning agents and machines, textiles, athletic apparel, dyes/paints, varnishes, polymers, and in medical products and applications. Given these diverse applications, nano silver is likely entering the environment. Several scientific studies describe potential adverse effects of nano silver on publicly owned treatment works (wastewater collection, treatment, and disposal systems).

Silver has been known historically as a potent antibacterial, antifungal, and antiviral agent. In recent years, silver is used as a biocide in solution, suspension, and in nano-particulate form. The strong antimicrobial activity is a major reason for the development of products that contain nano silver. Nano silver may also have applications in agricultural, vector, and urban pest control. However, little or no information about detecting and measuring the effect of nano silver in the environment exists. Recent published papers point out difficulties in quantifying the existence of nano particles in environmental and biological contexts, which presents challenges in estimating and assessing the hazards and risks of nano silver. [emphasis mine]

Nowack, one of the Empa researchers, provides evidence for his position in a commentary that was previously published in the journal Science (from the news item),

A commentary by Bernd Nowack in the scientific journal Science discusses the implications of the newest studies on nanosilver in sewage treatment plants. More than 90% remains bound in the sewage sludge in the form of silver sulfide, a substance which is extremely insoluble and orders of magnitude less poisonous than free silver ions. [emphasis mine] It apparently does not matter what the original form of the silver in the wastewater was, whether as metallic nanoparticles, as silver ions in solution or as precipitated insoluble silver salts.

“As far as the environmental effects are concerned, it seems that nanosilver in consumer goods is no different than other forms of silver and represents only a minor problem for eco-systems,” says Nowack. What is still to be clarified, however, is in what form the unbound silver is present in the treated water released from sewage works, and what happens to the silver sulfide in natural waters. Is this stable and unreactive or is it transformed into other forms of silver? [emphasis mine]

The two approaches are not directly contradictory but I do find the totality confusing. Which challenges about the hazards and risks of nano silver are the folks in California referring to? It seems they’re not familiar with the older research cited by Nowack or perhaps they know something Nowack and his colleagues do not. Meanwhile, Nowack’s Science commentary is reassuring but whoever wrote the news item was careful to point out that there is still some important work to be done before declaring nano silver to be a ‘safe’ substance.

I posted about the DTSC call for information, Feb. 7, 2011.